1. Field of the Invention
Embodiments relate generally to the field of treatment of aqueous solutions. More particularly, embodiments concern the use of electrodialysis for selective separation of ions from regeneration of solid ion-removal material such as, for example, ion-exchange resins.
2. Description of Related Art
Solid ion-removal material such as ion exchange resins are commonly used for selective removal of dissolved ions from water. Certain of these dissolved ions, whether in the form of cations or anions, are particularly undesirable. For example, calcium and magnesium ions increase the “hardness” of the water and sulfate ions contribute to corrosion and scaling problems in industrial applications. These ions are commonly found in water extracted from mining operations, making disposal of this water problematic. Ion exchange resin beads are used selectively to absorb cations or anions onto the resin beads and in so doing become progressively loaded with contaminant ions. Regeneration of these resin beads therefore becomes necessary in order to remove the contaminant ions from the resin.
Salt solutions are often used for regeneration of ion-exchange resins that are employed for removing valuable or objectionable ions from aqueous solutions. For example in water softening, the resins are used to remove hardness ions (such as calcium, magnesium, strontium, radium, and barium ions) from water and would become substantially saturated with the hardness ions over time of use. Usually highly concentrated solution of salt like NaCl may be used to regenerate the resins to displace hardness ions from the resins, and a spent regenerant with residual salt and mostly hardness ions will be produced. The spent regenerant is usually then discarded.
Although NaCl is not very expensive, its disposal can be problematic in some places. For example, discharging that spent regenerant containing salt to the local sewer, water body or the ground results in an increase in the salinity of the receiving body. If residual salt in the spent regenerant could be recycled, then the discharge would comprise primarily the hardness ions that are removed from the original water. A water softening system that has less salt in the discarded brine would be advantageous to the environment. However, recycling salt from the spent regenerant could be expensive and time consuming.
Therefore, there remains a need to develop methods and systems to address the problems in recycling spent regenerant from salt-regeneration of solid ion-removal material such as ion exchange resins.